(a) Field of the Invention
The present invention relates to an improvement in a package substrate, and more particularly to a light emitting die package substrate with good thermal conductivity, high heat dissipation, separate electrical and thermal paths and a simple and firm structure, and to an improvement in a package substrate in which the light from the light emitting dies can be reflected by a polished reflective layer to enhance the light availability.
(b) Description of the Prior Art
A chip on board (COB) package for packaging typical dies is a type of integrated circuit package, in which bare dies are directly attached to and packaged on a printed circuit board, or a copper substrate or an aluminum substrate. The combination of three basic manufacturing processes: die attaching, wire connecting and encapsulating can effectively transfer the packaging and testing steps during an IC manufacturing process direct to a circuit board assembly stage. This packaging technology is actually a miniature surface mounting technology.
Metal wires are used to connect the contacts of the dies to the contacts of a circuit board or a substrate to form the electrical connection. The encapsulation technologies are applied to cover the exterior thereof.
For this reason, this chip on board packaging technology has been applied to various consumer electronics, such as multifunction business machines, mobile phones, digital cameras and computers. This is also an important manufacturing process to make various consumer electronics toward miniaturization and multifunctionalization. In particular, a light emitting chip is taken as an example of a chip on board package structure of typical dies. As shown in FIG. 1, there is a cross-sectional side view of the prior art. It is apparent from the figure that in a traditional package structure, light emitting dies 11 are directly positioned on a substrate 12 (for example, a copper substrate, an aluminum substrate or another metal substrate, etc.), and an insulator 13 is applied on the substrate 12. In doing so, conductive segments 14 can be arranged on the insulator 13 of the substrate 12, and wires 15 are electrically connected from the contacts of the light emitting dies 11 to the conductive segments 14 on the insulator 13 by wire bonding. Subsequently, the above light emitting dies 11 and conductive segments 14 are encapsulated to form a chip on board package structure of light emitting dies.
However, such structure still has the drawback of high heat resistance. With increase in the performance of the light emitting dies 11, relatively, they generate heat increasingly. If there is no good way for dissipating the heat generated by and accumulated in the light emitting dies 11, the excessive temperature will lead to electronic ionization and thermal stress in the light emitting dies 11, thus reducing the overall stability and shortening the life of the light emitting dies 11 themselves. Therefore, in order to dissipate the heat to prevent the light emitting dies 11 from overheating, there is proposed a design of the following structure. As shown in FIGS. 2 and 3, there is a cross-sectional side view of another light emitting die package of the prior art. A circuit board 21 in which a metal sheet 22 is embedded as a structure for attaching dies, wire bonding and packaging, comprises a circuit board 21, a metal sheet 22 and light emitting dies 23. The circuit board 21 is provided with corresponding tapered open holes 211, and soldering points 212 are disposed on the surface of the circuit board 21 beside the corresponding holes 211. The soldering points 212 and the circuit board 21 are designed as an electrically connected circuit. The metallic trenches 221 formed by processing the metal sheet 22 are embedded in the corresponding holes 211 of the circuit board 21. The bottom of the metallic trench 221 protrudes from the corresponding hole 211 of the circuit board. The top edge of the metallic trench 221 is provided with openings 222 corresponding to the positions of the soldering points 212 of the circuit board 21 to allow the soldering points 212 to be exposed to air. The light emitting die 23 is attached into the metallic trench 221 followed by wire bonding to electrically connect the light emitting die 23 with the soldering points 212. Finally, the light emitting die 23 and the wires 24 are encapsulated in the metallic trench 221 to complete the light emitting die packaging process.
Nevertheless, there are still many shortcomings in the above light emitting die package structure during use, such as high material cost, difficulty in processing and low yield of final products due to complexity of manufacture and the like.